Calcium levels in Mr. Gallariani's blood are dropping to dangerously low levels. The hormone PTH is released

Question:

Calcium levels in Mr. Gallariani's blood are dropping to dangerously low levels. The hormone PTH is released and soon blood calcium levels begin to rise. Shortly after, PTH release slows. Is this an example of a positive or negative feedback mechanism? What is the initial stimulus? What is the result?